Clad material and method of manufacturing the material

ABSTRACT

The present invention, which is aimed at providing a method for manufacturing a clad material that can be used for the anode cases and cathode cases of button-type microbatteries and other miniature electronic devices requiring the use of comparatively thin, drawable sheets, allows the difference between r values, or Lankford values (which characterize the plastic anisotropy between the rolling/bonding direction of a clad material and a direction at a prescribed angle to the rolling/bonding direction) to be reduced by preforming cold rolling at a reduction of 30% or lower in addition to performing a conventional method for manufacturing a clad material, making it possible to substantially enhance the mechanical strength of the clad material and to mass-produce clad materials that have low reduction anisotropy.

TECHNICAL FIELD

The present invention relates to a readily drawable clad material havingexcellent tensile strength and other mechanical strength characteristicsand to a manufacturing method therefor and, in particular, makes itpossible to provide a clad material for the anode cases or cathode casesof button-type microbatteries, cases for quartz oscillators, cases forvarious other electronic components, and other types of miniatureelectronic equipment that require deep drawability.

BACKGROUND ART

Clad materials obtained by bonding a plurality of metals through rollingare integrated materials that preserve the characteristics ofindividual, metals, and are hence extremely useful in applications inwhich a plurality of characteristics must be provided at the same time.

For example, cases for button-type microbatteries must have the desiredmechanical strength, drawability, corrosion resistance, low contactresistance, and the like. CU/SUS (stainless steel)/Ni, Cu/Fe/Ni, andother clad materials are used for anode cases; and Ni/SUS, Ni/SUS/Ni,Al/SUS/Ni, and other clad materials are used for cathode cases.

In addition, Ni/Fe/Ni, Ni/SUS/Ni, Cu/SUS/Ni, Cu/Fe/Ni, and other cladmaterials are used for the cases of various electronic components thathave specific requirements concerning mechanical strength, drawability,corrosion resistance, weldability, and the like.

Clad materials that function as base materials for such cases arecommonly obtained by superposing a plurality of metal sheetsconstituting a clad material, bonding these sheets by cold rolling,homogenizing the sheets, and subjecting them to finish cold rolling or acombination of finish cold rolling and final annealing. The product maybe optionally cut into prescribed lengths.

Clad materials obtained by the aforementioned manufacturing method aremolded into cup shapes by conventional deep drawing, making it possibleto obtain cases designed for various applications and fashioned tospecific dimensions.

For example, miniaturization of cases for the aforementioned button-typemicrobatteries becomes crucial because of the need for smaller andlighter devices in the field of electrical equipment.

Specifically, demand for thinner clad material increases because of theneed to design cases for smaller button-type microbatteries that havehigher capacity and longer life. Conventionally at about 0.2˜0.3 mm,device thickness is currently being reduced to about 0.1˜0.15 mm.

It has been confirmed that conventional manufacturing methods make itdifficult to perform deep drawing as desired even when the goal islimited to obtaining a thin clad material. Specifically, the inventorshave performed experiments and confirmed that an attempt to obtain aclad material by a conventional manufacturing method results in a highLankford value, or a considerable difference between r values (whichcharacterize the plastic anisotropy between the rolling/bondingdirection and a direction at a prescribed angle to the rolling bondingdirection). In addition, deep drawing produces low roundness and yieldsan oval shape whose major axis is oriented in the rolling/bondingdirection. In particular, cracks and ruptures form and a cup shape isdifficult to obtain when a thin clad material is formed.

SUMMARY OF THE INVENTION

With the foregoing problems in mind, it is an object of the presentinvention to provide a readily drawable clad material having excellenttensile strength and other mechanical strength characteristics, and anmanufacturing method therefore and, in particular, to a clad materialsuitable for use as an anode case or cathode case for button-type microbatteries and for other applications involving miniature electronicdevices and requiring deep drawability and the use of comparatively thinsheets, and a manufacturing method therefor.

As a result of repeated experiments aimed at attaining the statedobject, the inventors perfected the present invention upon discoveringthat the difference between r values (which characterize the plasticanisotropy between the rolling bonding direction of a clad material anda direction at a prescribed angle to the rolling/bonding direction) canbe reduced by performing cold rolling at a rolling reduction of 30% orlower in addition to performing a conventional method for manufacturinga clad material, making it possible to substantially enhance themechanical strength of the clad material and to mass-produce cladmaterials that have low reduction anisotropy.

Specifically, the present invention resides in a clad materialcharacterized in that metal cladding is rolled/bonded to at least oneprincipal surface of a metal substrate, and a value of less than 0.6 isset for the maximum difference between the r values (measured under 5%elongation) expressing the plastic anisotropy between therolling/bonding direction, a direction at 45° to the rolling/bondingdirection, and a direction at 90° to the rolling/bonding direction.

Another feature of the above-described clad material is that a value of0.7 or greater is set for the r values that express the plasticanisotropy between the rolling/bonding direction, a direction at 45° tothe rolling/bonding direction, and a direction at 90° to therolling/bonding direction.

Yet another feature of the above-described clad material is that thecombined thickness is set to 0.5 mm or less, and the thickness of themetal cladding is set to between 2 and 20% of the thickness of the metalsubstrate.

Still another feature of the above-described clad material is that themetal substrate is stainless steel and that the Goss {110}<100>-orientedaccumulation in the plane in which bonding with the metal cladding isachieved is less than that observed when no metal cladding isrolled/bonded. An additional feature of the clad material is that themetal cladding is at least one material selected from copper and nickel.

The manufacturing method for obtaining the above-described clad materialis characterized in that a clad material obtained by the rolling/bondingof metal cladding to at least one principal surface of a metal substrateis subjected to cold rolling at a rolling reduction of 30% or lower, andpreferably 5 to 25%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting the relation between the yield strength,tensile strength, and angle with respect to the rolling/bondingdirection, where FIG. 1A depicts measurements obtained following coldrolling at a rolling reduction of 82%, FIG. 1B those obtained followingfinal annealing, and FIG. 1C those obtained following cold rolling at arolling reduction of 25%;

FIG. 2 is a graph depicting the relation between the r value and theangle with respect to the rolling/bonding direction, where FIG. 2Adepicts measurements obtained following final annealing, and FIG. 2Bthose obtained following cold rolling at a rolling reduction of 25%;

FIG. 3 is a graph depicting the crystal orientation distributionfunction (ODF) of the clad material cold-rolled at a rolling reductionof 25%;

FIG. 4 is a graph depicting the crystal orientation distributionfunction (ODF) of a single SUS sheet;

FIG. 5 is a graph depicting the relation between the r value and theangle with respect to the rolling/bonding direction, obtained using amethod for estimating the r values of a polycrystalline material fromODF on the basis of the Taylor theory proposed by Bunge;

FIG. 6 is a graph depicting the relation between the r value and therolling reduction of the clad material; and

FIG. 7 is a graph depicting the relation between the Euler angles andthe orientation density, where FIG. 7A depicts the α-fiber and β-fiberof an SUS clad material, and FIG. 7B depicts the α-fiber and β-fiber ofa single SUS sheet.

BEST MODE FOR CARRYING OUT THE INVENTION

No particular restrictions are imposed on the properties of the metalsubstrate or metal cladding constituting the clad material of thepresent invention. As a result of experiments conducted by theinventors, it was confirmed that irrespective of the properties of themetal substrate and the metal cladding, the manufacturing method of thepresent invention yields lower reduction anisotropy as a result of thefact that the r value (which indicates the plastic anisotropy of themetal substrate itself) remains substantially constant in allrolling/bonding directions, and the non-uniformity of the r value isreduced, yielding an r value that remains substantially unchangedthroughout the clad material, and ultimately making it possible toperform highly accurate deep drawing.

As follows from the below-described results of a study into the textureof surfaces along which clad materials comprising SUS (stainless steel)as the metal substrate and copper or nickel as the metal cladding arebonded to the metal cladding, the Goss {110}<100>-oriented accumulationis much less pronounced and orientation dispersion is comparatively highin comparison with a case in which no metal cladding is rolled/bonded.The formation of a texture having such comparatively pronouncedorientation dispersion is believed to be the reason for the reducednon-uniformity of the r value.

Although the extent to which aggregation occurs in a specificorientation varies somewhat with the properties of the metal substrate,the texture of the entire clad material still has comparatively highorientation dispersion, and the same effect can be attained.

The metal cladding is not necessarily rolled/bonded to both principalsurfaces of the metal substrate. The material should be selectedaccording to the intended application and rolled/bonded to one or bothprincipal surfaces. The above-described effect can thus be obtained forthe principal surfaces of a metal substrate to which this clad materialis rolled/bonded.

In particular, conventional stainless steel SUS (austenitic stainlesssteel, ferritic stainless steel, two-phase stainless steel, orprecipitation-hardened stainless steel), iron, 30˜55 wt % Ni—Fe, 20˜60wt % Ni—Cu, 25˜50 wt % Ni-5˜20 wt % Co—Fe, and the like shouldpreferably be used as the metal substrates of clad materials for theanode cases or cathode cases of button-type microbatteries and othertypes of miniature electronic equipment because of considerationsrelated to mechanical strength, thermal stability, consistency ofthermal expansion coefficient, weldability, and the like. In addition,nickel, copper, aluminum, 5˜30 wt % Cr—Ni, 20˜60 wt % Ni—Cu, and thelike should preferably be used as metal claddings because ofconsiderations related to corrosion resistance, electrical resistance,bondability, and the like.

The metal substrate and metal cladding should preferably be differentmaterials in order to make the effect of the present invention morepronounced.

The desired effect of the present invention can be obtained irrespectiveof the combined thickness of the clad material, but this material shouldpreferably be used in applications having the above-describeddrawability and reduced thickness requirements in order to best utilizethe effect of the present invention. The combined thickness of the cladmaterial should be 0.5 mm or less, preferably 0.3 mm or less, andideally 0.2 mm or less.

Although the thickness ratio of the metal substrate and metal claddingconstituting the clad material is not subject to any particularlimitations, it is preferable that the thickness of the metal claddingconstitute no more than 2%, and preferably no more than 20%, of thethickness of the metal substrate in order to work the manufacturingmethod described below.

When metal cladding is rolled/bonded to both principal surfaces of ametal substrate, the desired effect can be obtained by satisfying theabove-described conditions for the metal cladding rolled/bonded to atleast one principal surface, although it is best for the metal claddingrolled/bonded to both principal surface to satisfy the aforementionedconditions. The effect of the present invention can be attained withmaximum efficiency through suitable selection of the thickness ratio ofthe metal substrate and metal cladding in accordance with the combinedrequired thickness of the clad material.

As referred to herein, the r values that characterize the plasticanisotropy between the rolling/bonding direction, a direction at 45° tothe rolling/bonding direction, and a direction at 90° to therolling/bonding direction are values measured by the method defined inASTM-E517 and based on the use of samples cut in a direction parallel toeach direction. The r values and elongation can be expressed by Eqs. 1and 2 below $\begin{matrix}{r = \frac{\ln \left( {w_{0}/w} \right)}{\ln \left( {{{LW}/L_{0}}w_{0}} \right)}} & {{Eq}.\quad 1} \\{{Elongation} = {\frac{L - L_{0}}{L_{0}} \times 100(\%)}} & {{Eq}.\quad 2}\end{matrix}$

where w₀ is the width of an undeformed sheet, w is the width of adeformed sheet, L₀ is the undeformed gage length, and L is the deformedgage length.

Specifically, the clad material obtained by a common method inaccordance with the present invention is subjected to cold rolling at arolling reduction of 30% or lower, so the clad material itself undergoeswork hardening, and its elongation decreases. Commonly, the r values aremeasured at an elongation of 15˜20%. In the present invention, the rvalues are measured at an elongation of 5%.

When a value of 0.6 or greater is set for the maximum difference betweenthe resulting r values characterizng the plastic anisotropy in therollinglbonding direction, a direction at 45° to the rolling/bondingdirection, and a direction at 90° to the rolling/bonding direction,higher reduction anisotropy results, and the desired deep drawing cannotbe performed. In particular, the aforementioned maximum differencebetween the r values should be set to 0.5 or lower in order to obtainhighly accurate deep drawing.

Essentially, the higher the r value, the better the drawability, so avalue of 0.7 or greater, and particularly 1.0 or greater, should beselected from within the above-described non-uniformity range for therolling/bonding direction, a direction at 45° to the rolling/bondingdirection, and a direction at 90° to the rolling/bonding direction.

Tensile strength and yield strength, which are used as standards forevaluating the metal substrate of the clad material of the presentinvention, are measured by the method described in JIS Z 2241. Inparticular, not only does the clad material of the present inventionhave higher tensile strength and yield strength than does a conventionalclad material (as will become apparent from the embodiments describedbelow), but the characteristics of the material remain substantially thesame in any direction, irrespective of its relation to therolling/bonding direction.

The above-described method for obtaining a clad material in accordancewith the present invention is characterized in that a clad materialobtained by the rolling/bonding of metal cladding to at least oneprincipal surface of a metal substrate in the manner described aboveundergoes further cold rolling at a rolling reduction of 30% or lower.

A conventional manufacturing method comprises steps in which a pluralityof metal substrates constituting a clad material are superposed,rolled/bonded in the cold state, homogenized, and subjected to finishcold rolling or a combination of finish cold rolling and finalannealing.

The manufacturing method of the present invention can be performed suchthat a clad material subjected to the aforementioned finish cold rollingis then heat-treated within a prescribed temperature range andcold-rolled at a rolling reduction of 30% or lower, and the cladmaterial that has undergone finish cold rolling and final annealing ismerely cold-rolled at a rolling reduction of 30% or lower.

The initial rolling/bonding step is not limited to the aforementionedcold rollingtbonding, and the same effect can be obtained by adoptingwarm rolling/bonding or hot rolling/bonding. It is not always necessaryto perform homogenizing and finish cold rolling, and the need for aparticular step should be selected together with specific conditions orthe like in accordance with the properties, thickness, and otherattributes of the metal substrate and metal cladding.

It is also possible to perform scratching/brushing and other surfacetreatments prior to the final rolling/bonding step, to use a tensionleveler for thickness readjustment or to perform otherthickness-adjusting treatments following cold rolling at a rollingreduction of 30% or lower, or to add other conventional steps.

Specifically, a basic feature of the present invention is that the cladmaterial is cold-rolled at a rolling reduction of 30% or lower duringthe final step of obtaining this material and that a heat treatment isoptionally performed prior to the cold rolling. The present inventionalso encompasses arrangements in which the heat treatment and the coldrolling at the rolling reduction of 30% or lower are performed aplurality of times in accordance with the properties, thickness, andother attributes of the metal substrate and metal cladding.

The optionally performed heat treatment may be performed under the sameconditions as the aforementioned fmal annealing, and optimum conditionsshould be selected in accordance with the properties, thickness, andother attributes of the metal substrate and metal cladding. Thetreatment is commonly performed within a range of 500 to 1100° C.

The rolling reduction during the above-described cold rolling must bekept at 30% or lower because when the rolling reduction exceeds 30%,excessively small elongation results, much lower drawability isestablished, and the difference (non-uniformity) between the r valuesreaches or surpasses 0.6. In particular, the r value in therolling/bonding direction (0° direction) is 0.7 or lower. The rollingreduction should preferably be 5˜30%, and particularly 5˜25%, becausemechanical strength is reduced and the difference (non-uniformity)between the r values reaches or surpasses 0.6 when the rolling reductionis made lower than necessary.

In addition, a metal cladding prevents a metal substrate from cominginto direct contact with the work rolls of the rolling mill during therolling/bonding of the metal cladding to the metal substrate and thesubsequent rolling thereof, and is believed to improve texture formationby the plastic deformation of the metal substrate, functioning ag aso-called frictional buffer. Consequently, the thickness of the metalcladding should preferably constitute at least 2% of the thickness ofthe metal substrate. In addition, the thicknes of the metal claddingshould commonly be selected at no more than 20% of the thickness of themetal substrate because making the metal cladding excessively thickcauses the clad material to lose some of its mechanical strength as awhole.

EMBODIMENTS

The effect of the present invention will now be described through a theembodiments that follow.

Embodiment 1

A Cu/SUS/Ni clad material with a thickness of 0.15 mm was prepared asthe clad material of the present invention. The SUS used as the metalsubstrate corresponded to SUS304 (JIS G 4307), the copper used as themetal cladding rolled/bonded to one principal surface corresponded toC1020 (JIS H 3100), and the nickel used as the metal claddingrolled/bonded to the other principal surface corresponded to VN/R (JIS H4501). The ultimate thicknesses were as follows: 123 μm (82%) for theSUS, 24 μm (16%) for the copper, and 3 μm (2%) for the nickel. Thenumbers in parentheses following the μm units designate the thicknessratios.

The SUS (metal substrate), copper, and nickel (metal claddings) wereprepared, and a three-layer clad material with a thickness of 1.1 mm wasobtained by subjecting these components to cold rolling/bonding andhomogenization. The material was then cold-rolled at a rolling reductionof 82%, subjected to final annealing at 1000° C., and cold-rolled at arolling reduction of 25%, yielding the above-described clad material ofthe present invention.

To demonstrate the effect of the proposed clad material, a single SUSsheet used as a metal substrate was fabricated according to the samehistory as a comparison material.

The clad material of the present invention and the comparison materialcomposed of a single SUS sheet were subjected to final annealing andcold rolling at a rolling reduction of 25%, and the resulting sampleswere used to measure tensile strength, yield strength, r values, andtexture attributes.

The vertical axes of the graphs in FIGS. 1A, 1B, and 1C indicate tensilestrength and yield strength, and the horizontal axes indicate the anglewith respect to the rolling/bonding direction (the angle of thedirection parallel to the rolling/bonding direction is assumed to be 0°(deg.)). The solid lines between the black circles indicate the tensilestrength of the clad material, the broken lines between the blackcircles indicate the yield strength of the clad material, the solidlines between the white circles indicate the tensile strength of thesingle SUS sheet, and the broken lines between the white circlesindicate the yield strength of the single SUS sheet. In addition, FIG.1A depicts measurements obtained following cold rolling at a rollingreduction of 82%, FIG. 1B those obtained following final annealing, andFIG. 1C those obtained following cold rolling at a rolling reduction of25%.

The samples for measuring tensile strength and yield strength had thefollowing measurements: a gage length of 50 mm, a width of 12.5 mm, andthicknesses of 0.2 mm (following cold rolling at a rolling reduction of82% and final annealing) and 0.15 mm (following cold rolling at arolling reduction of 25%).

It follows from the graph in FIG. 1 that the clad material of thepresent invention (see FIG. 1C) has higher tensile strength and yieldstrength than does the finish cold rolling following final annealing(see FIG. 1B), that these values are similar, and that the values in therolling/bonding direction (0° direction), a direction at 45° to therolling/bonding direction, and a direction at 90° to the rolling/bondingdirection are substantially the same and vary only slightly. It can thusbe confirmed that the clad material of the present invention has theadvantage of low anisotropy with respect to mechanical strength.

The vertical axes of the graphs in FIGS. 2A and 2B indicate the r value,and the horizontal axes indicate the angle with respect to therolling/bonding direction (the angle of the direction parallel to therolling/bonding direction is assumed to be 0° (deg.)). The thick solidlines between the black circles indicate the r values of the cladmaterial, the dashed lines between the white circles indicate the rvalues of SUS, which is the metal substrate obtained by removing copperand nickel (metal claddings) from the clad material by etching them withan acid, and the broken lines between the white squares indicate the rvalues of the single SUS sheet. FIG. 2A depicts measurements obtainedfollowing final annealing, and FIG. 2B those obtained following coldrolling at a rolling reduction of 25%.

The samples for measuring the r values had the following measurements: agage length of 50 mm, a width of 12.5 mm, and thicknesses of 0.2 mm(following final annealing) and 0.15 mm (following cold rolling at arolling reduction of 25%). Measurements were conducted at an elongationof 5% in the manner described above.

It follows from FIG. 2A that the r value produced by final annealing ishigh in the direction in which the angle is 45° with respect to therolling/bonding direction and that this trend is particularly pronouncedin the single SUS sheet. The non-uniformity (maximum difference) of ther values is 0.6 or greater, and about 1 for a single SUS sheet.

It follows from FIG. 2B that the r value following cold rolling at arolling reduction of 25% is high not only in the direction in which theangle is 45° with respect to the rolling/bonding direction, but also inthe 90° direction. This trend is pronounced in a single SUS sheet, andthe drop is particularly noticeable in the rolling/bonding direction (0°direction). The non-uniformity (maximum difference) of the r values isabout 0.3 in a clad material, and about 0.7 in a single SUS sheet.

To confirm the effect of a metal cladding on a clad material, r valueswere measured after the copper and nickel clad materials had been etchedoff, leaving the SUS metal substrate alone. It was possible to confirmthat the r values did not differ much under conditions corresponding tothe use of a clad material.

It follows from these graphs that the non-uniformity of the r values inthe clad material of the present invention is less than that of a cladmaterial subjected to final annealing. It can also be seen that thenon-uniformity is 1.0 or greater in the rolling/bonding direction (0°direction), where the r value is the lowest.

Consequently, it can be confirmed that the clad material of the presentinvention is advantageous in the sense of making it possible tofabricate nearly-round cases of low plastic anisotropy while preventingcracks, ruptures, or the like from forming during drawing.

The above-described effect is more pronounced than in the case of asingle SUS sheet, and it can be demonstrated that the features of thepresent invention can be found only in clad materials.

FIGS. 3 and 4 are crystal orientation distribution functions (ODFs)calculated by series expansion based on surface harmonics, usingincomplete pole figures (reflection-method α_(max)=75°) for the {111},{100}, {110}, and {311} orientations of a single SUS sheet (FIG. 4) anda clad material (FIG. 3) cold-rolled at a rolling reduction of 25%.Euler angle notation is in accordance with the Bunge definition.

The drawings indicate the present of β-fibers all the way from thecopper {112}<111>orientation to the Bs {011}<211>orientation through theS {123}<634>orientation for both the clad material and the single SUSsheet. Although some α-fibers or weak cubic orientation could also beperceived, it was confirmed that the Goss {110}<100>-orientedaccumulation was about twice as strong for the clad material,particularly when a single SUS sheet was involved. In other words, it isclear that FIG. 7A depicts the relation between the Euler angle and theorientation density for an SUS304 clad material, and FIG. 7B depicts thesame relation for a single SUS sheet.

In addition, the r value is high in the direction in which the anglewith respect to the rollingfbonding direction is 90°, and low in the 0°direction. The tendency of the Goss-oriented accumulation to increase ismore pronounced for the single SUS sheet. It can thus be assumed thatthe non-uniformity of r values is considerable for a single SUS sheetand, in particular, the r value is very low in the rolling/bondingdirection (0° direction).

FIG. 5 depicts results obtained by calculating r values from theaforementioned ODFR, that is, results obtained using a method forestimating the r values of a polycrystalline material from an ODF on thebasis of the Taylor theory proposed by Bunge. In the drawing, the thicksolid lines between the black circles indicate the r values calculatedfor a clad material, and the broken lines between the white circlesindicate the r values calculated for a single SUS sheet. The r valuesthus calculated are relatively high and can be demonstrated to be insatisfactory qualitative agreement with measured values.

Embodiment 2

An SUS metal substrate and copper and nickel metal claddings wereprepared in the same manner as in Embodiment 1; and Cu/SUS/Ni cladmaterials with a thickness of 0.15 mm were fabricated by performing coldrolling/bonding, homogenization, cold rolling, and final annealing,followed by cold rolling under variable rolling reduction (0˜35%).

The r values of the clad materials obtained under variable rollingreduction were measured by the same method as in Embodiment 1. Theresults are shown in FIG. 6. In the graph shown in FIG. 6, the verticalaxis indicates the r values; the horizontal axis, rolling reduction.

In the drawing, the solid lines between the solid circles indicate the rvalues in the rolling/bonding direction (0° direction), the broken linesbetween the white circles indicate the r values in the direction at anangle of 45° to the rollingibonding direction of the clad materials, andthe solid lines between the white circles indicate the r values in thedirection at an angle of 90° to the rolling/bonding direction of theclad materials.

It can be seen in FIG. 6 that the non-uniformity (maximum difference) inthe r values in the rolling/bonding direction (0° direction), the 45°direction, and the 90° direction is less than 0.6, and all the r valuesare 0.7 or greater when the rolling reduction is no more than 30%. Whenthe rolling reduction is 35%, the r values increase as such and becomehighly non-uniform.

The fact that the non-uniformity of r values again increases when therolling reduction is near 0% suggests that the rolling reduction shouldbe kept at 30% or lower, preferably 5˜30%, and ideally 5˜25%, in orderto attain the object of the present invention.

Embodiment 3

To evaluate the drawability of the proposed clad material, an SUS metalsubstrate and copper and nickel metal claddings were prepared; coldrolling/bonding, homogenization, cold rolling, and final annealing wereperformed; cases measuring 5 mm in outside diameter and 7 mm in heightwere fabricated using a Cu/SUS/Ni clad material (thickness: 0.3 mm)cold-rolled at a rolling reduction of 25%, a single SUS sheet(thickness: 0.3 mm) cold-rolled at a rolling reduction of 25%, and aCu/SUS/Ni clad material (thickness: 0.3 mm) cold-rolled at a rollingreduction of 35%; and cracking, rupturing, and roundness were measured.The results are snown in Table 1.

It follows from Table 1 that the clad material of the present inventioncan yield near-round cases having minimal reduction anisotropy.

TABLE 1 Material Rolling (thickness ratio (%)) reduction DrawabilityRoundness Cu/SUS/Ni(16/82/2) 25% Good  5 μm Single SUS sheet 25% Fair 12μm Cu/SUS/Ni(16/82/2) 35% Fair 15 μm

Embodiment 4

To evaluate the drawability of the proposed clad material, an SUS metalsubstrate and copper and nickel metal claddings were prepared; coldrolling(bonding, homogenization, cold rolling, and final annealing wereperformed; cases measuring 5 mm in outside diameter and 7 mm in heightwere fabricated using a Cu/SUS/Ni clad material (thickness: 0.15 mm)cold-rolled at a rolling reduction of 25%, a single SUS sheet(thickness: 0.15 mm) cold-rolled at a rolling reduction of 25%, and aCu/SUS/Ni clad material (thickness: 0.15 mm) cold-rolled at a rollingreduction of 35%; and cracking, rupturing, and roundness were measured.The results are shown in Table 2.

It follows from Table 2 that the clad material of the present inventioncan yield near-round cases having minimal reduction anisotropy.

TABLE 2 Material Rolling (thickness ratio (%)) reduction DrawabilityRoundness Cu/SUS/Ni(16/82/2) 25% Good  6 μm Single SUS sheet 25% Fair 15μm Cu/SUS/Ni(16/82/2) 35% Rupturing occurred —

Embodiment 5

To evaluate the drawability of the proposed clad material, an SUS metalsubstrate and a nickel metal cladding were prepared; coldrolling/bonding, homogenization, cold rolling, and final annealing wereperformed; cases measuring 5 mm in outside diameter and 7 mm in heightwere fabricated using an NVlSUS clad material (thickness—0.15 mm)cold-rolled at a rolling reduction of 25%, a single SUS sheet(thickness: 0.15 mm) cold-rolled at a rolling reduction of 25%, and anNi/SUS clad material (thickness: 0.15 mm) cold-rolled at a rollingreduction of 35%; and cracking, rupturing, and roundness were measured.The results are shown in Table 3.

It follows from Table 3 that the clad material of the present inventioncan yield near-round cases having minimal reduction anisotropy.

TABLE 3 Material Rolling (thickness ratio (%)) reduction DrawabilityRoundness Ni/SUS/(5/95) 25% Good  8 μm Single SUS sheet 25% Fair 15 μmNi/SUS/(5/95) 35% Rupturing occurred —

Embodiment 6

To evaluate the drawability of the proposed clad material, an SUS metalsubstrate and copper and nickel metal claddings were prepared; coldrolling/bonding, homogenization, cold rolling, and final annealing wereperformed; cases measuring 5 mm in outside diameter and 7 mm in heightwere fabricated using a Cu/SUS/Ni clad material (thickness: 0.1 mm)cold-rolled at a rolling reduction of 25%, a single SUS sheet(thickness: 0.1 mm) cold-rolled at a rolling reduction of 25%, and aCu/SUS/Ni clad material (thickness: 0.1 mm) cold-rolled at a rollingreduction of 35%; and cracking, rupturing, and roundness were measured.The results are shown in Table 4.

It follows from Table 4 that the clad material of the present inventioncan yield near-round cases having minimal reduction anisotropy.

TABLE 4 Material Rolling (thickness ratio (%)) reduction DrawabilityRoundness Cu/SUS/Ni(7/91/2) 25% Good 8 μm Single SUS sheet 25% Repturingoccurred — Cu/SUS/Ni(7/91/2) 35% Rupturing occurred —

Embodiment 7

To evaluate the drawability of the proposed clad material, an SUS metalsubstrate was prepared, as was nickel overlaid as a metal cladding onthe two principal surfaces of the metal substrate; cold rolling/bonding,homogenization, cold rolling, and final annealing were performed; casesmeasuring 5 mm in outside diameter and 7 mm in height were fabricatedusing an Ni/SUS/Ni clad material (thickness: 0.1 mm) cold-rolled at arolling reduction of 25%, a single SUS sheet (thickness: 0.1 mm)cold-rolled at a rolling reduction of 25%, and an Ni/SUS/Ni cladmaterial (thickness: 0.1 mm) cold-rolled at a rolling reduction of 35%;and cracking, rupturing, and roundness were measured. The results areshown in Table 5.

It follows from Table 5 that the clad material of the present inventioncan yield near-round cases having minimal reduction anisotropy.

TABLE 5 Material Rolling (thickness ratio (%)) reduction DrawabilityRoundness Ni/SUS/Ni(2/96/2) 25% Good 9 μm Single SUS sheet 25% Rupturingoccurred — Ni/SUS/Ni(2/96/2) 35% Cracking —

INDUSTRIAL APPLICABILITY

The embodiments described above demonstrate that the clad materialobtained in accordance with the present invention has excellentdrawability and exceptional tensile strength and other metal substratecharacteristics, and can thus be used for the anode cases or cathodecases of button-type microbatteries and other miniature electronicdevices requiring the use of comparatively thin, drawable sheets.

The material also has excellent weldability, corrosion resistance, andother merits. The clad material of the present invention can be used notonly in the aforementioned battery cases but also in quartz oscillatorssimilar in shape and size to battery cases, and in various otherelectronic components, and hence has very high commercial value.

What is claimed is:
 1. A clad material formed by rolling/bonding a metalcladding to at least one principal surface of a metal substrate in arolling/bonding direction, wherein the maximum difference between theLankford values (r values, measured under 5% elongation) expressing theplastic anisotropy between the rolling/bonding direction, a direction at45° to the rolling/bonding direction, and a direction at 90° to therolling/bonding direction, is less than 0.6.
 2. The clad material asdefined in claim 1, wherein the r values that express the plasticanisotropy between the rolling/bonding direction, a direction at 45° tothe rolling/bonding direction, and a direction at 90° to therollingfbonding direction are greater than 0.7.
 3. The clad material asdefined in claim 1, wherein the thickness of the entire material is 0.5mm or less.
 4. The clad material as defined in claim 3, wherein thethickness of the metal cladding is between 2 and 20% of the thickness ofthe metal substrate.
 5. The clad material as defined in claim 1, whereinthe metal substrate is stainless steel, and the Goss {110}<100>-orientedaccumulation in the plane in which bonding with the metal cladding isachieved is less than that observed when no metal cladding isrolled/bonded.
 6. The clad material as defined in claim 5, wherein themetal cladding is at least one material selected from the groupconsisting of copper and nickel.
 7. A method for manufacturing a cladmaterial comprising the step of cold rolling at a rolling reduction of30% or lower a metal cladding to at least one principal surface of ametal substrate, and wherein a maximum difference between Lankfordvalues (r values measured under 5% elongation) which express plasticanisotropy between a rolling/bonding direction and directions at 45°thereto and 90° thereto is less than 0.6.
 8. The method formanufacturing a clad material as defined in claim 7, wherein the rollingreduction of cold rolling is 5˜25%.
 9. The clad material as defined inclaim 2, wherein the thickness of the entire material is set to 0.5 mmor less.